<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <!-- Copyright David Abrahams 2006. Distributed under the Boost --> <!-- Software License, Version 1.0. (See accompanying --> <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> <html> <head> <meta name="generator" content= "HTML Tidy for Cygwin (vers 1st April 2002), see www.w3.org"> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" type="text/css" href="../boost.css"> <title>Boost.Python - <boost/python/return_arg.hpp></title> </head> <body> <table border="0" cellpadding="7" cellspacing="0" width="100%" summary= "header"> <tr> <td valign="top" width="300"> <h3><a href="../../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3> </td> <td valign="top"> <h1 align="center"><a href="../index.html">Boost.Python</a></h1> <h2 align="center">Header <boost/python/return_arg.hpp></h2> </td> </tr> </table> <hr> <h2>Contents</h2> <dl class="page-index"> <dt><a href="#introduction">Introduction</a></dt> <dt><a href="#classes">Classes</a></dt> <dd> <dl class="page-index"> <dt><a href="#return_arg-spec">Class Template <code>return_arg</code></a></dt> <dd> <dl class="page-index"> <dt><a href="#return_arg-spec-synopsis">Class Template <code>return_arg</code> synopsis</a></dt> <dt><a href="#return_arg-spec-statics">Class <code>return_arg</code> static functions</a></dt> </dl> </dd> <dt><a href="#return_self-spec">Class Template <code>return_self</code></a></dt> </dl> </dd> <dt><a href="#examples">Example</a></dt> </dl> <hr> <h2><a name="introduction"></a>Introduction</h2> <code>return_arg</code> and <code>return_self</code> instantiations are models of <a href="CallPolicies.html">CallPolicies</a> which return the specified argument parameter (usually <code>*this</code>) of a wrapped (member) function. <h2><a name="classes"></a>Classes</h2> <h3><a name="return_arg-spec"></a>Class template <code>return_arg</code></h3> <table border="1" summary="return_arg template parameters"> <caption> <b><code>return_arg</code> template parameters</b> </caption> <tr> <th>Parameter</th> <th>Requirements</th> <th>Description</th> <th>Default</th> </tr> <tr> <td><code>arg_pos</code></td> <td>A positive compile-time constant of type <code>std::size_t</code>.</td> <td>the position of the argument to be returned.</td> <td>1</td> </tr> <tr> <td><code>Base</code></td> <td>A model of <a href="CallPolicies.html">CallPolicies</a></td> <td>Used for policy composition. Any <code>result_converter</code> it supplies will be overridden by <code>return_arg</code>, but its <code>precall</code> and <code>postcall</code> policies are composed as described here <a href= "CallPolicies.html#composition">CallPolicies</a>.</td> <td><code><a href= "default_call_policies.html#default_call_policies-spec">default_call_policies</a></code></td> </tr> </table> <h4><a name="return_arg-spec-synopsis"></a>Class template <code>return_arg</code> synopsis</h4> <pre> namespace boost { namespace python { template <size_t arg_pos=1, class Base = default_call_policies> struct return_arg : Base { static PyObject* postcall(PyObject*, PyObject* result); struct result_converter{ template <class T> struct apply; }; template <class Sig> struct extract_return_type : mpl::at_c<Sig, arg_pos>{}; }; }} </pre> <h4><a name="return_arg-spec-statics"></a>Class <code>return_arg</code> static functions</h4> <pre> PyObject* postcall(PyObject* args, PyObject* result); </pre> <dl class="function-semantics"> <dt><b>Requires:</b> <code><a href= "http://www.python.org/doc/2.2/api/tupleObjects.html#l2h-476">PyTuple_Check</a>(args) != 0</code> and <code>PyTuple_Size(args) != 0</code></dt> <dt><b>Returns:</b> <code>PyTuple_GetItem(args,arg_pos-1)</code></dt> </dl> <h3><a name="return_self-spec"></a>Class template <code>return_self</code></h3> <h4>Class template <code>return_self</code> synopsis:</h4> <pre> namespace boost { namespace python { template <class Base = default_call_policies> struct return_self : return_arg<1,Base> {}; }} </pre> <h2><a name="examples"></a>Example</h2> <h3>C++ module definition</h3> <pre> #include <boost/python/module.hpp> #include <boost/python/class.hpp> #include <boost/python/return_arg.hpp> struct Widget { Widget() :sensitive_(true){} bool get_sensitive() const { return sensitive_; } void set_sensitive(bool s) { this->sensitive_ = s; } private: bool sensitive_; }; struct Label : Widget { Label() {} std::string get_label() const { return label_; } void set_label(const std::string &l){ label_ = l; } private: std::string label_; }; using namespace boost::python; BOOST_PYTHON_MODULE(return_self_ext) { class_<widget>("Widget") .def("sensitive", &Widget::get_sensitive) .def("sensitive", &Widget::set_sensitive, return_self<>()) ; class_<Label, bases<Widget> >("Label") .def("label", &Label::get_label) .def("label", &Label::set_label, return_self<>()) ; } </pre> <h3>Python code</h3> <pre> >>> from return_self_ext import * >>> l1 = Label().label("foo").sensitive(false) >>> l2 = Label().sensitive(false).label("foo") </pre> <p>Revised <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> 19 July, 2003 <!--webbot bot="Timestamp" endspan i-checksum="39359" --> </p> <p><i>© Copyright <a href= "http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> and Nikolay Mladenov 2003. </i></p> </body> </html>